It is known to provide electrosurgical generators which provide different radio frequency (RF) power signals for cutting and coagulation, and also to switch between two different instruments, e.g. bipolar and monopolar instruments. In a first type of prior art system, it is also known to provide an electrosurgical instrument with a single electrode, and switching means on the instrument to connect the electrode alternately to either a cutting output or to a coagulating output from the generator. Examples of these types of instrument are to be seen in U.S. Pat. Nos. 4,427,006, 5,376,089 and 5,573,424.
Alternatively, in a second type of prior art system, it is known to provide an instrument with multiple electrodes, and to provide switching means on the instrument to be able to connect the power signal from the generator to different electrodes or combinations of electrodes. Examples of this type of instrument are to be seen in U.S. Pat. Nos. 5,269,780 and 5,951,551. The disadvantage of all of these prior art systems is that it is not possible to optimize both the signal supplied by the generator and the choice of electrodes. In the case of the first type of prior art system, the use of a single electrode means that its design must always be a compromise between designs suited to cutting and those suited to coagulation. In the case of the second type of prior art, the instrument uses the same output power signal from the generator for whichever combination of electrodes is deployed. U.S. Pat. No. 6,270,497 discloses a device which switches between coagulation and cutting operations, but which is relatively complicated in design.
U.S. Pat. No. 7,204,835 discloses an clectrosurgical instrument in which a pair of forceps jaws are provided with a third electrode, designed to effect the electrosurgical cutting of tissue. Such designs have the electrosurgical cutting electrode as a longitudinal rail running along the middle of one of the jaws. An alternative design is shown in U.S. Pat. No. 6,984,231, which has the electrosurgical cutting electrode as a “nipple” positioned on the outside of one of the jaws.
The present invention attempts to provide an improvement to each of these prior designs, and to provide an instrument capable of effective cutting and coagulation, even in the very restricted spaces encountered in endoscopic surgery.